My proposal is concerned with the regulation of actin patterns in cells and how these patterns provide movement. More specifically, I propose to study the controls over actin assembly using as a model the acrosomal reaction of echinoderm sperm. The five proteins that regulate the assembly of actin will be isolated, characterized and made to function in vitro. By fast freezing and rotary shadowing techniques, I will examine intermediates in the elongation of the acrosomal process. Motion generated by changes in twist of the actin helix as seen in the acrosomal reaction of Limulus sperm will be studied in more detail using morphological techniques coupled with diffraction analysis and by looking at the location of the three proteins making up this bundle. I also propose to examine the formation of bundles of actin filaments in the stereocilia of the inner ear to establish how these bundles form developmentally and what might regulate the lengths of the actin filaments. And finally, I plan to examine dividing cells to determine the number, distribution and polarity of the actin filaments in the "contractile ring" using fast freezing and rotary shadowing techniques.